Method of treating phosphate coated surfaces



uNlrao srAras PATENT orric mt'mon or 'rnca'rma mosrm'ra coa'ran soar-sons Bertha s. Tattle, Newton, and Thaddeus Navoy,

Jamaica Plain, Mesa, usignors to J. N. Tattle, 1:12., Ntt'ewton, Mann, a corporation of Mallamet No Drawing. Application April 27, 1944,

Serial No. 533,062

. 16 Claims. 1

This invention relates to a method of treating phosphate-coated surfaces, such as are commonly applied to ferrous and ferrous alloy articles, to increase their corrosion resistance and if desired to impart a color thereto.

It has long been known that zinc, cadmium and ferrous surfaces may be rendered more or less corrosion resistant by treatment with phosphoric acid and/or phosphates of such metals as manganese, iron, zinc, copper and combinations thereof, with or without oxidizing agents or depolarizers, etc., typical procedures being disclosed in U. S. Patents No. 1,651,694 and No. 1,- 911,726, each of which embodies the use of a compound having the empirical formula M(HzPO4)2, wherein M may be a metal from manganese to cadmium in the electromotive series. Since the essential ingredient embodied in such treatments is the phosphate radical, the processes are generally referred to as phosphate treatments, being commercially known as Parkerizing, Bonderizing, Granodizing, etc. It has also been found that the efficacy of the phosphate treatment may be enhanced and the character of the resultant phosphate coating varied by the use of salts of metals below iron in the electromotive series, and to this end minor amounts of salts of such elements as copper, silver, lead, tin, antimony,

arsenic, etc., along with the principal ingredient, e. g.,' M(H2PO4)2, have been suggested. However, in all such modified procedures the essential or primary ingredient is the metal phosphate which provides at least the major-portion of the corrosion resistant coating, the other ingredients being of secondary importance in that they either concomitantly form an additional phosphate complex along with the principal phosphate coating, or function apparently as an accelerator, catalyst or the like.

Such processes are generally unsatisfactory without supplementary treatments such as oiling, waxing, painting, etc., principally because they do not provide a high degree of corrosion resistance. A further deficiency in the phos phate treatment as commercially practiced is that it does not readily and satisfactorily permit fast coloring of the treated surface other than by the application of a coat of paint or lacquer, which inevitably results in objectionable dimensional changes.

The principal objects of the present invention are to provide a composition for and method of treating phosphate-coated surfaces so as greatly to increase their corrosion resistance; to provide a composition for and method of simultaneously increasing the corrosion resistance of phosphate coated articles and imparting thereto a desired coloration which can not 'be rubbed or washed off, which does not produce appreciable dimensional changes and which is relativel fast to light; and to provide a protective phosphate coating which is denser, more adherent, refined and smoother than the phosphate coatings heretofore produced, and which is resistant to heat and generally more attractive.

Further objects will be apparent from a consideration of the following description wherein we have disclosed several illustrative examples of what is now considered a preferred procedure embodying the use of typical compositions coming within the scope of the present invention.

We have found that articles having a phosphate coating such as produced by any of the well-known commercial treated with an aqueous solution of a stannous salt which reacts with the phosphate coating to produce a highly resistant, smooth, dense coating consisting essentially of a tin-metalphosphatecomplex, which has a corrosion resistance many times greater than that produced by any of the procedures heretofore used, as indicated by the standard salt spray test; and that if a compatible dye be incorporated in the stannous salt solution, the dye apparently becomes chemically combined with the tin-metal-phosphate complex and the resultant coating not only is given a coloration which is relatively fast to'light and unaffected by water and solvents, but also is rendered more corrosion resistant than the tin-metal-phosphate coating without the dye. We have also found that by incorporating in the stannous salt solution certain stabilizers or inhibitors such as mannitol, gum arabic, dextrose and the like soluble carbohydrates, gelatine and similar hydrophilic colloids, the corrosion resistance of the resultant coating is likewise greatly increased.

In accordance with the present invention, the material to be treated, for example an article composed of iron, steel, a ferrous alloy, etc., is first subjected to any treatment capable ofproducing a phosphate coating, and to this end the article may be treated in accordance with any of the well known commercial procedures such, for example, as are disclosed in U. S. Patents Nos. 1,007,069, 1,651,694 and.1,911,726. The phosphate coating thus produced consists essentially of a relatively insoluble porous crystalline film-like structure formed on or: integral with the surface of the treated article, and, without supplemenprocedures may be s tary treatment suchas oiling, waxing.'etc.. has,

more i a corrosion resistance oi the order of two to six temperature which may vary from room temperature'to the boiling point of the solution and for a period which may vary from a few seconds to severalminutes, depending upon the particular stanncus salt used, the character of the basic phosphate coating, and the desired degree of core rosion resistance. The resultant coating is the reaction product of the stanncus salt and the original phosphate coating and consists essentially of a tin-metal-phosphate complex which is not only smoother, more dense, flue-grained and scratch resistant than the phosphate coating base, but also many'times more corrosion resistant. If it be desired to produce a greater corrosion resistance and/or coloring of the'resultant coating, a dye soluble in and compatible with the stanncus salt solution may be incorporated in the treating bath or solution, and in either case. if desired, a suitable stabilizer or inhibitor may also be added to the treating solution. The resultant coating consists essentially of a tin-metal-phosphate-dye complex which not only possesses increased corrosion resistance, as compared to the tin-metal-phosphate coating, but also an attractive coloration which is relatively fast to light and heat, and unafl'ected by water and solvents, and furthermore does not undergo an objectionable darkening when treated with oil and wax. After having completed the above treatment, with or without coloration, the article may then be rinsed off, dried, and, if desired, oiled or waxed in accordance with conventional practices.

The stanncus salts suitable for use in our process are limited to those that are water soluble and relatviely stable, and whose acidity may, if necessary, be adjusted so that the phosphate coating base is not stripped. Such salts comprise the stanncus halides, stanncus sulphate, stannous fiuoborate, and certain organic stanncus salts. such as the acetate, oxalate and tartrate. Practical considerations, however, indicate the use of the chloride, viz., SnCla.2HsO, which has been found most satisfactory when used in concentrations varying from less than 1% to the Thus the dyes which are compatible are those which are soluble. in an aqueous 5% stanncus chloride solution without causing the format-ion of substantial precipitate or undergoing discoloration during a substantial'period, e. g. one hour. Among the dyes which have been tested and found to be satisfactory are the following:

Identification or M of Colour Index No.

Ant uinone Green 1078 Alkali est Green... 735 Bairauine T (l 841 Rhodaminc D 752 Allzarin Red 8 (3)- 1034 Wool Fast Blue 833 c Green L 666 Acid Green B 667 Wool Violet 1BN. NB Alisarine Blue GRL. 1088 Alphazurins FG Anthraquinone Blue RXO Methylene Blue on All dyes above listed, except those followed by a parenthetical numerical notation, are classified as acid dyes. The notations designate the following classifications:

(1) Azine basic type (2) Phthalic anhydride type (3) Mordant acid type (4) Acid and basic type (5) Basic type (6) Unclassified The amount or concentration of the dye will depend on'the particular dye and the depth of saturation point of the salt, although preferred working limits are between 2 and The dye or coloring agents suitable for use in our process include the synthetic organic dyestuffs and certain animal and vegetable dyes which are compatible with an aqueous stanncus salt solution having an acid pH. Recognized classifications of dyes, such as are found in the Colour Index (edited by F. M. Rowe and published under the auspices of the Society of Dyers and Colourists), off little or no assistance in determining the particular types of dyes which are operative or suitable in our process. (In general dyes containing 2.20 and nitro groups are inoperative, while the acid dyes of the triphenylmethane and xanthene types are operative.) However, the operability of any particular dye may readily be determined, and as a practical matter should be checked, by testing its compatibility with an aqueous 5% stannous chloride solution. If the dye causes the formation of a precoloration desired, but as a general rule from 0.1% to 10%, based on the weight of the treating solution, which is equivalent to a minimum of 0.4% of dye based on the weight of stanncus salt within the above range, constitute practical working limits. However small quantities of other compatible dyes may be added for'shading. The use of a. stabilizer or inhibitor may be desired, particularly where maximum corrosion resistance is of the utmost importance, and to this end the treating bath or solution may include such stabilizers or inhibitors as mannitol, gum arable, dextrose, sugar and the like carbohydrates, or gelatine and other types of hydrophilic colloids. However, it should be understood that the use of a stabilizer or inhibitor, although sometimes advisable, is generally unnecessary,

, and where the use of a stabilizer is indicated, the

amount to be used may, as a. practical matter, vary between 10% and 40%, based on the weight of the stannous salt, depending upon the length of the period during which the treating solution or bath is to be used.

A procedure illustrative of the foregoing is as follows:

Example 1.A stanncus salt solution is first cipitate or becomes discolored it is incompatible. 76 prepared by dissolving parts (by weight) of commercial stannous chloride in 1000 parts of water, after which the solution is brought to boiling. Metallic tin may, if desired, be added to stabilize the bath, although satisfactory results may be secured without such addition. Steel, iron or other ferrous metal pieces, previously phosphate coated in conventional manner employing the Parkerizing Process, are then dipped in the stannous chloride for approximately one minute while at boiling temperature, after which the pieces are removed, rinsed and dried. A smooth, fine-grained, dense coating having a gray coloration is produced.

Example 2.-The procedure set forth in Example 1 was followed, except'that parts of Fast- Acid Green B dye were incorporated in the stannous chloride solution with the result that a dark green coloration, fast to light and washing, was imparted to the coating.

Example 3.The procedure set forth in Ex ample 1 was followed, except that 10 parts of mannitol were added to the stannous chloride 2 and 4 to 6) indicated that the coloration a g I Further tests on the dyed coatings (Examples was fast to strong light, water and solvents.

In order to determine whether or not the incorporation of the dye in the stannous salt solution, as in Examples 2 and 4 to 6, produced results appreciably diiferent from those obtained by treating phosphate-coated pieces, as in Example 1, and subsequently subjecting the pieces to a dip in a hot 1% dye solution, a series of tests were conducted in which (a) different dyes were incorporated in the stannous chloride solution following the procedure set forth in Example 2,

and a second series oftests were conducted in which (b) the pieces were treated as in Example 1 and then dipped in a hot dye solution containing the same amount of dye as the coorrespond-. ing test under (a). The following table shows the treatments and. the results obtained, it bein understood that the examples'marked a follow the procedure of Example 2 and those marked b follow the procedure of-Example 1 with a subsesolution. The appearance of the coating was quent dye dip:

Example Dye Coloration Salt Spray Test 70 Acid Green L Medium Green--... Greater than 1251mm, 7b do ver Light Green-.. 40 hours maximum. 80 Acid Green B Dar Green... Greater than 125 hours.

50 hours maximum.

70 to 90 hours. Dark Uneven Stain- 40 hours maximum.

100 AlizarineBlue GRL.... Very Light Blue.... 70 hours. 100 do Colorless hours maxim 11a Alphazurine FG Light Blue-Green... 90 hours. 11b ..do I T Pale Bluish 40 hours. I 120.-.-.- Quinolene Yellow Light Green-Yellow- Greater than 70 hours. 121) do No coloration 35 hours maximum. I

Dark Green-Blue--. Greater than 70 hours. Light Blue 50 hours maximum. Red-Violet Greater than 70 hours. Light Violet Tint... 40 hours maximum.

substantially the same as that produced by Example 1.

Example 4.--The-procedure set forth in Ex-- ample 2 was followed using 10 parts of Wool Green S and 2 parts of sodium carbonate in place of the East Acid Green B. The resultant coating was similar to that produced by Example 1, except the coloration was a dark green-blue.

Example 5.The same procedure as set forth, in Example 2 was followed using 0 parts of Quinolene Yellow and the resultant coating had a light green-yellow coloration.

Example 6.The same procedure set forth in Example 2 was followed using approximately 10 parts of a dye mixture which produced a coatin having an olive drab coloration. 1

The pieces treated by each of the above procedures, without supplementary treatment, were then subjected to the standard salt spray test,

. along with the untreated phosphate-coated pieces, and the results are shown in the following table:

, ing is appreciably different, thus clearly indicating that the action of the'dye when incorporated in thestannous salt solution is at least much more eflicacious, i. e., not only imparting the desired coloration to the coating, but also greatly increasing its resistance to corrosion, than when dipped into a dye Anthraquinone G, Alkali Fast Green 2G, Safranine T, Rhodamine 6GDN, Alizarine Fast Blue,

and Wool Fast Blue.

Examples representative of other stannous salt solutions as as follows:

Ezample 15.'-A stannous salt solution was first prepared by dissolving 50 parts (by weight) of stannous sulfate in 1000 parts of water, after which 13 parts of sodium carbonate were added. A piece of ferrous metal having a phosphate coating was then dipped into the treating solution for aperiod of ten minutes during which the solution was maintained at boiling temperature. A smooth, fine-grained, dense coating, comparable to that of Example 1, was produced. Salt spray tests showed an initial corrosion resistance of 15 hours as compared to 2-3 hours for the untreated phosphate coating, a corrosionresistance rating after 33 hours of 7, as compared to a rating of 3 for the untreated coating, and a 7 70 hours.

corrosion resistance of greater than 60 hours for the treated piece, as compared to 15' hours for the untreated piece.

Example 16.-A stannous sulfate solution was prepared as in Example 15, and 10 parts of Fast Acid Green 13 were added thereto. A piece of ferrous metal having a phosphate coating was then subjected to treatment as in Example 15,

'withthe result'that a dark green coloration, fast to light and washing,-was produced. The coating showed an initial corrosion resistance of 33 hours and substantial rusting after more than 70 hours.

Example 17.A stannous sulfate treating solution was prepared as in Example 16, except that 12.5 parts of sodium carbonate and 10 parts of Wool Green S were used. The phosphate coated metal was treated for ten minutes at boiling temperature with the result that a coating having a blue green coloration was produced. This coating showed an initial corrosion resistance of approximately 35 and substantial rusting after l hours.

Example 18.-A stannous salt solution was prepared by dissolving 50 parts of stannous fiuoborate in 1000 parts of water, after which parts of sodium carbonate was added. A phosphate coated piece of ferrous metal was then dipped into the solution maintained at boiling temperature for one minute. A coating comparable to that of Example 1 .was produced, which had an initial corrosion resistance or 6 to 15 hours and substantial rusting after 50 hours.

Example 19.-A stannous fiuoborate solution was prepared as in Example 18, and 10 parts of Fast Acid Green B were added to the solution. The test pieces were dipped for one minute in the solution while maintained at boiling temperature. A colored coating similar to that of Example 16 was produced, which coating had an initial corrosion resistance of approximately hours with substantial rusting after more than Example 20.-A stannous fiuoborate solution was prepared as in Example 19, except that 10 parts of Wool Green S were added instead of the Fast Acid Green B. The test pieces were dipbed in the treating .solution for five minutes while maintained at boiling temperature. The

resultant coating was comparable to that of Example 17, having a corrosion resistance, better than that of Example 8, but less than that of Example 19.

All salt spray tests, herein referred to, were made on unoiled test pieces so that the eificacy of the various treatments could be determined more accurately. It is to be understood, however, that such supplementary treatments as oiling, waxing, etc., will substantially increase the corrosion resistance of both the untreated phosphate coated pieces and those treated in accordance with the present invention.

Experiments using organic stannous salts, viz., the acetate, oxalate and tartrate, with and without dyes, indicate that these salts are likewise efilcacious in greatly increasing the corrosion re-.

sistance and producing a coloration which is relatively fast to light, heat and solvents.

The foregoing definitely indicates that a stannous salt solution alone is capable of greatly increasing the corrosion resistance of phosphatecoated ferrous metals and alloys, and that when used in conjunction with a compatible dye, it not only produces a further increase in corrosion radical with the metal surface.

vantageous feature of our treatment is that itmay be carried out in a short time, c. g., a minute or two, and in a single operation. If desired. both the general appearance and corrosion resistance may be further enhanced by oiling, waxing or the like conventional treatment.

We claim:

1. The method of treating a metal article having an insoluble'metalphosphate coating thereon produced by chemical reaction of the phosphate which comprises subjecting said phosphate coating to the action of an aqueous solution of a stannous salt which is water soluble and water stablepthe solution having an acidity insuillcient to strip said phosphate coating, thereby to form an insoluble tinmetal-phosphate complex having a corrosion resistzince greatly exceeding the original phosphate coa ng.

2. The method of treating a metal article hav ing an insoluble metal phosphate coating thereon produced by chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to the action of an aqueous stannous chloride solution, the solution having an acidity insumcient tostrip said phosphate coating, thereby to form an insoluble tin-metal-phosphate complex having a corrosion resistance greatly exceeding the original phosphate coating.

3. The method of treating metallic articles which comprises first forming a phosphate coating thereon by treatment with an aqueous solution containing a salt having the general formula M(H2PO4)2, wherein M is a metal in the electromotive series from manganese to iron, both inclusive and subsequently subjecting said phosphate coating to the. action of an aqueous solution of a stannous salt which is water soluble and water stable, the solution having an acidity insufilcient to strip said phosphate coating, and thereby to form an insoluble tin-metal-phosphate complex having a corrosion resistance greatly exceeding the original phosphate coating.

4. The method of treating metallic articles which comprises first forming a phosphate coating thereon by treatment with an aqueous solution containing a salt having the general formula M(H:PO4) wherein M is a metal in the electromotive series from manganese to iron, both inclusive and subsequently subjecting said phosphate coating to the action of an aqueous stannous chloride solution, the solution having an acidity insufllcient to strip said phosphate coating, thereby to form an insoluble tin-metal-phosphate complex having a corrosion resistance greatly exceeding the original phosphate coating.

5. The method of treating a metal article having an insoluble metal phosphate coating thereon produced by chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to the action of an aqueous solution of a stannous salt phosphate coat ng.

which is water soluble and water stable, the solution having an' acidity insufilcient tostrip said and a dye compatible with said stannous salt solution thereby to form an 6. The method of treating a metal article having an insoluble metal phosphate coatin thereon produced by chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to the action of an aqueous stannous chloride solution and a dye compatible with said stannous chloride solu-' tion, the solution having an acidity insuflicient to strip said phosphate coating, thereby to form an insoluble tin-metal-phosphate-dye complex having a corrosion resistance greatly exceeding the original phosphate coating and simultaneously imparting a coloration thereto.

.7. The method of treating a metal article having an insoluble metal phosphate coatin thereon produced by chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to the action of an aqueous treating solution containing from 2% to of a stannous salt which is water soluble and water stable, the solution having an acidity insufllcient to strip said phosphate coating, thereby to form an insoluble tin-metal-phosphate complex having a corrosion resistance greatly exceeding the original phosphate coating.

8. The method of treating a metal article having an insoluble metal phosphate coating thereon produced by chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to the action of an aqueous treating solution containing from 2% to 25% of a stannous chloride, the solution having -an acidity insumcient to strip said phosphate coating, thereby to form an insci uble tinmetal-phosphate complex having a corrosion re sistance greatly exceeding the original phosphate coating.

9. The method of treating metallic articles which comprises first forming a phosphate coating thereon by treatment with an aqueous solution containing a salt having the general formula M(H2PO4)2, wherein M is a metal in the electromotive series from manganese to iron, both in-' clusive and subsequently subjecting said phosphate coating to the action of an aqueous treating solution containing from 2% to 25% of a stannous salt which is water soluble and water stable, the solution having an acidity insuficient to strip said phosphate coating, thereby to form an insoluble tin-metal-phosphate complex having a corrosion resistance greatly exceeding the original phosphate coating.

10. The method of treating metallic articles which comprises first forming a phosphate coating thereon by treatment with an aqueous solution containing a salt having the general formula M(H2PO4)2, wherein M is a metal in the electromotive series from manganese to iron, both inclusive and subsequently subjecting said phosphate coating to the action of a. treating solution containing 2% to 25% stannous chloride, the solution having an acidity insufflcient to strip said phosphate coating, thereby to form an insoluble tin-metal-phosphate complex having a corrosion resistance greatly exceeding the original phosphate coating.

11. The method of treating a metal article having an insoluble metal phosphate coating thereon 10 producedby chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to the action of an aqueous treating solution containing from 2% to 25% of a stannous salt which is water soluble and water stable, the solution having an acidity insufllcient to strip said phosphate coating, and from 0.1% to 10% (based on the weight of the treating solution) of a dye compatible with said stannous salt solution, thereby to form an insoluble tin-metal-phosphate-dye' complex having a corrosion resistance greatly exceeding the original phosphate coating.

12. The method of treating a metal article having an insoluble metal phosphate coating thereon produced by chemical reaction of the phosphate radical with the metal surface, which comprises subjecting said phosphate coating to the action of an aqueous treating solution containing from 2% to 25% ofstannous chloride and from 0.1% to 10% (based on the weight of the treating solution) of a dye compatible with said stannous chloride solution, the said stannous chloride solution having an acidity insufllcient to strip said phosphate coating thereby to form an insoluble tin-metal-phosphate-dye complex having a corrosion resistance greatly exceeding the original phosphate coating.

13.;An article having a protective coating consisting essentially of an insoluble tin-metal-phosphate complex produced in accordance with the process of claim 1.

14. An article having a protective coating consisting essentially of an insoluble tin-metal-phosphate complex produced in accordance with the process of claim 3. w

15. An article having a protective coating consisting essentially of an insoluble tin-metal-phosphate-dye complex produced in accordance with the process of claim 5;

16. An article having a protective coating consisting essentially of an insoluble tin-metal-phosphate complex produced in accordance with the process of claim 9.

BERTHA S. TU'I'ILE.

THADDEUS NAVOY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,303,627 Baines May 13, 1919 1,329,573 Allen Feb. 3, 1920 1,426,675 Schlotter Aug. 22, 1922 1,466,126 Fink Aug. 28, 1923 1,514,494 Williams Nov. 4, 1924 1,694,820 Harris Dec. 11, 1928 2,200,615 Boyle May 14, 1940 2,236,549 Darsey et a1. Apr. 1, 1941 2,295,063 Tuttle Sept. 8, 1942 2,304,299 Boyle et a1 Dec. 8, 1942 2,314,565 Thompson Mar. 23, 1943 FOREIGN PATENTS Number Country Date 731,994 lirance June 6, 1932 OTHER REFERENCES Cox: Hair Dyes. I. The chemistry and analysis of henna, The Analyst (England) vol. 63 (1938), pages 397-404. 

